Provided by: libnetpbm11-dev_10.97.00-2_amd64 
NAME
libppm - functions for PPM programs
SYNOPSIS
#include <netpbm/ppm.h>
void ppm_init(int * argcP,
char * argv[]);
pixel ** ppm_allocarray(
int cols,int rows);
pixel * ppm_allocrow(int cols);
void ppm_freearray(pixel ** pixels,
int rows);
void ppm_freerow(pixel * pixelrow);
void ppm_readppminit(FILE * fp,
int * colsP,
int * rowsP,
pixval * maxvalP,int * formatP );
void ppm_readppmrow(FILE *fp,
pixel * pixelrow,
int cols,
pixval maxval,
int format);
pixel ** ppm_readppm(FILE * fp,
int * colsP,
int * rowsP,
pixvalP * maxvalP);
void ppm_writeppminit(FILE * fp,
int cols,
int rows,
pixval maxval,
int forceplain);
void ppm_writeppmrow(FILE * fp,
pixel * pixelrow,
int cols,
pixval maxval,
int forceplain);
void ppm_writeppm(FILE * fp,
pixel ** pixels,
int cols,
int rows,
pixval maxval,
int forceplain);
void ppm_writeppm(FILE * fp,
pixel ** pixels,
int cols,
int rows,
pixval maxval,
int forceplain);
void ppm_nextimage(FILE * file,
int * const eofP);
void ppm_check(FILE * file,
const enum pm_check_type check_type,
const int format,
const int cols,
const int rows,
const int maxval, enum pm_check_code * const retval);
typedef ... pixel;
typedef ... pixval;
#define PPM_MAXMAXVAL ...
#define PPM_OVERALLMAXVAL ...
#define PPM_FORMAT ...
#define RPPM_FORMAT ...
#define PPM_TYPE PPM_FORMAT
#define PPM_FORMAT_TYPE(format) ...
pixval PPM_GETR(pixel p)
pixval PPM_GETG(pixel p)
pixval PPM_GETB(pixel p)
void PPM_ASSIGN(pixel p,
pixval red,
pixval grn,
pixval blu)
int PPM_EQUAL(pixel p,
pixel q)
int PPM_ISGRAY(pixel p)
void
PPM_DEPTH(pixel newp,
pixel p,
pixval oldmaxval,
pixval newmaxval)
pixel ppm_parsecolor(char * colorname,
pixval maxval)
pixel ppm_parsecolor2( char * colorname, pixval maxval, int closeOk )
char * ppm_colorname(pixel * colorP,
pixval maxval,
int hexok)
void ppm_readcolornamefile(
const char *fileName,
int mustOpen,
colorhash_table * chtP,
const char *** colornamesP
)
DESCRIPTION
These library functions are part of Netpbm(1).
TYPES AND CONSTANTS
Each pixel contains three pixvals, each of which should contain only the values between 0
and PPM_MAXMAXVAL.
MANIPULATING PIXELS
The macros PPM_GETR, PPM_GETG, and PPM_GETB retrieve the red, green, or blue sample,
respectively, from the given pixel.
The PPM_ASSIGN macro assigns the given values to the red, green, and blue samples of the
given pixel.
The PPM_EQUAL macro tests two pixels for equality.
The PPM_ISGRAY macro tests a pixel for being gray. It returns true if and only if the
color of pixel p is black, white, or gray.
The PPM_DEPTH macro scales the colors of pixel p according the old and new maxvals and
assigns the new values to newp. It is intended to make writing ppmtowhatever easier.
The PPM_LUMIN, PPM_CHROM_R, and PPM_CHROM_B macros determine the luminance, red
chrominance, and blue chrominance, respectively, of the pixel p. The scale of all these
values is the same as the scale of the input samples (i.e. 0 to maxval for luminance,
-maxval/2 to maxval/2 for chrominance).
Note that the macros do it by floating point multiplication. If you are computing these
values over an entire image, it may be significantly faster to do it with multiplication
tables instead. Compute all the possible products once up front, then for each pixel,
just look up the products in the tables.
INITIALIZATION
ppm_init() is obsolete (at least since Netpbm 9.25 (March 2002)). Use pm_proginit()
⟨libpm.html#initialization⟩ instead.
ppm_init() is identical to pm_proginit.
MEMORY MANAGEMENT
ppm_allocarray() allocates an array of pixels.
ppm_allocrow() allocates a row of the given number of pixels.
ppm_freearray() frees the array allocated with ppm_allocarray() containing the given
number of rows.
ppm_freerow() frees a row of pixelss allocated with ppm_allocrow().
READING FILES
If a function in this section is called on a PBM or PGM format file, it translates the PBM
or PGM file into a PPM file on the fly and functions as if it were called on the
equivalent PPM file. The format value returned by ppm_readppminit() is, however, not
translated. It represents the actual format of the PBM or PGM file.
ppm_readppminit() reads the header of a PPM file, returning all the information from the
header and leaving the file positioned just after the header.
ppm_readppmrow() reads a row of pixels into the pixelrow array. format, cols, and maxval
are the values returned by ppm_readppminit().
ppm_readppm() reads an entire PPM image into memory, returning the allocated array as its
return value and returning the information from the header as rows, cols, and maxval.
This function combines ppm_readppminit(), ppm_allocarray(), and ppm_readppmrow().
WRITING FILES
ppm_writeppminit() writes the header for a PPM file and leaves it positioned just after
the header.
forceplain is a logical value that tells ppm_writeppminit() to write a header for a plain
PPM format file, as opposed to a raw PPM format file.
ppm_writeppmrow() writes the row pixelrow to a PPM file. For meaningful results, cols,
maxval, and forceplain must be the same as was used with ppm_writeppminit().
ppm_writeppm() write the header and all data for a PPM image. This function combines
ppm_writeppminit() and ppm_writeppmrow().
MISCELLANEOUS
ppm_nextimage() positions a PPM input file to the next image in it (so that a subsequent
ppm_readppminit() reads its header).
ppm_nextimage() is analogous to pbm_nextimage(), but works on PPM, PGM, and PBM files.
ppm_check() checks for the common file integrity error where the file is the wrong size
to contain all the image data.
ppm_check() is analogous to pbm_check(), but works on PPM, PGM, and PBM files.
COLOR
Luminance, Chrominance (YcbCr)
float PPM_LUMIN(pixel p);
float PPM_CHROM_B(pixel p);
float PPM_CHROM_R(pixel p);
PPM_LUMIN takes a pixel as an argument and returns the luminance of that pixel, with the
same maxval as the pixel (e.g. if the pixel's maxval is 255, a PPM_LUMIN value of 255
means fully luminant).
PPM_CHROM_B and PPM_CHROM_R are similar, for the red and blue chrominance values.
pixel
ppm_color_from_ycbcr(unsigned int y,
int cb,
int cr);
ppm_color_from_ycbcr() converts in the other direction. Given luminance and chrominance,
it returns a pixel value.
Hue, Saturation, Value (HSV)
struct hsv {
double h; /* hue (degrees) 0..360 */
double s; /* saturation (0-1) */
double v; /* value (0-1) */
};
pixel
ppm_color_from_hsv(struct hsv const hsv,
pixval const maxval);
struct hsv
ppm_hsv_from_color(pixel const color,
pixval const maxval);
These convert a color between from pixel (RGB) form and HSV.
pixval
ppm_saturation(pixel const p,
pixval const maxval);
This gives you the saturation of a color, as a pixval. (e.g. if the saturation of p is
50% and maxval is 100, ppm_saturation() returns 50).
Berlin-Kay Color
Brent Berlin and Paul Kay in 1969 did a study which identified a set of 11 basic colors
people universally recognize. They are:
• black
• gray
• white
• red
• orange
• yellow
• green
• blue
• violet
• purple
• brown
The bk_color type represents a color from this set:
typedef enum {
BKCOLOR_BLACK = 0,
BKCOLOR_GRAY,
BKCOLOR_WHITE,
BKCOLOR_RED,
BKCOLOR_ORANGE,
BKCOLOR_YELLOW,
BKCOLOR_GREEN,
BKCOLOR_BLUE,
BKCOLOR_VIOLET,
BKCOLOR_PURPLE,
BKCOLOR_BROWN
} bk_color;
You can use this as an index of an array, in which case you might also want macro
BKCOLOR_COUNT, which is the number of colors in the set (11).
To translate between the bk_color type and the English names of the colors, use
ppm_bk_color_from_name() and ppm_name_from_bk_color():
bk_color
ppm_bk_color_from_name(const char * name);
const char *
ppm_name_from_bk_color(bk_color bkColor);
ppm_bk_color_from_color() tells you to which Berlin-Kay color a certain color is closest,
by way of a fuzzy color matching algorithm:
bk_color
ppm_bk_color_from_color(pixel color,
pixval maxval);
maxval is the maxval on which color is based.
ppm_color_from_bk_color() converts the opposite way: given a Berlin-Kay color, it gives
the color, in pixel form, that best represents it.
pixel
ppm_color_from_bk_color(bk_color bkColor,
pixval maxval);
maxval is the maxval on which the returned color is based.
All of the facilities in this section were new in Netpbm 10.34 (June 2006).
COLOR NAMES
System Color Dictionary
Netpbm uses the system's X11 color dictionary (usually in /usr/lib/X11/rgb.txt). This is
the same file the X Window System typically uses to associate colors with their names.
The color dictionary that Netpbm uses is in the file whose name is the value of the RGBDEF
environment variable. If RGBDEF is not set, Netpbm defaults to the first existing file
from this list:
• /usr/lib/X11/rgb.txt
• /usr/openwinlib/rgb.txt
• /usr/X11R6/lib/X11/rgb.txt
You can see the color names from a typical X11 color dictionary, which is probably very
close to what is on your system, along with the colors, here
⟨http://www.swiss.ai.mit.edu/~jaffer/Color/x11.pdf⟩ . This website" (1) shows a bunch of
other versions you could use.
Netpbm is packaged with a color dictionary. A standard Netpbm installation installs this
file as "misc/rgb.txt" in the Netpbm directory. This color dictionary has colors from
everywhere the Netpbm maintainer could find them, and is a superset of XFree 86's color
dictionary.
ppm_parsecolor
ppm_parsecolor() interprets a color specification and returns a pixel of the color that it
indicates. It is the same as pnm_parsecolor ⟨libnetpbm_image.html#colorname⟩ , except
that it returns a pixel instead of a tuple.
ppm_parsecolor2
ppm_parsecolor2() interprets a color specification and returns a pixel of the color that
it indicates and warns about rounding. It is the same as pnm_parsecolor2
⟨libnetpbm_image.html#colorname⟩ , except that it returns a pixel instead of a tuple.
ppm_colorname
ppm_colorname() returns a string that describes the color of the given pixel. If a system
color dictionary ⟨#dictionary⟩ is available and the color appears in it, ppm_colorname()
returns the name of the color from the file. If the color does not appear in a system
color dictionary and hexok is true, ppm_colorname() returns a hexadecimal color
specification triple (#rrggbb). If a system color dictionary is available but the color
does not appear in it and hexok is false, ppm_colorname() returns the name of the closest
matching color in the color file. Finally, if there is no system color dictionary
available and hexok is false, ppm_colorname() fails and throws an error
⟨liberror.html#error⟩ .
The string returned is in static libppm library storage which is overwritten by every call
to ppm_colorname().
ppm_readcolornamefile
ppm_readcolornamefile() reads the entire contents of the color dictionary in the file
named fileName into data structures you can use to access it easily.
The function returns all the color names as an array of null-terminated strings. It
mallocs the space for this array and returns its address at colornamesP.
(*colornamesP)[i] is the address of the first character in the null-terminated string that
is the name of the ith color in the dictionary.
The function also returns a colorhash_table (see COLOR INDEXING ⟨#colorindex⟩ ) that
matches all these color names up to the colors they represent. It mallocs the space for
the colorhash_table and returns its address at chtP. The number that the colorhash_table
associates with each color is the index into the color name array described above of the
name of that color.
You may specify a null pointer for fileName to indicate the default color dictionary.
mustOpen is a boolean. If it is nonzero, the function fails and aborts the program if it
is unable to open the specified color dictionary file. If it is zero, though, it simply
treats an unopenable color dictionary as an empty one. The colorhash and color name array
it returns contain no colors or names.
ppm_readcolornamefile() was new in Netpbm 10.15 (April 2003).
COLOR INDEXING
Sometimes in processing images, you want to associate a value with a particular color.
Most often, that's because you're generating a color mapped graphics format. In a color
mapped graphics format, the raster contains small numbers, and the file contains a color
map that tells what color each of those small numbers refers to. If your image has only
256 colors, but each color takes 24 bits to describe, this can make your output file much
smaller than a straightforward RGB raster would.
So, continuing the above example, say you have a pixel value for chartreuse and in your
output file and you are going to represent chartreuse by the number 12. You need a data
structure that allows your program quickly to find out that the number for a chartreuse
pixel is 12. Netpbm's color indexing data types and functions give you that.
colorhash_table is a C data type that associates an integer with each of an arbitrary
number of colors. It is a hash table, so it uses far less space than an array indexed by
the color's RGB values would.
The problem with a colorhash_table is that you can only look things up in it. You can't
find out what colors are in it. So Netpbm has another data type for representing the same
information, the poorly but historically named colorhist_vector. A colorhist_vector is
just an array. Each entry represents a color and contains the color's value (as a pixel)
and the integer value associated with it. The entries are filled in starting with
subscript 0 and going consecutively up for the number of colors in the histogram.
(The reason the name is poor is because a color histogram is only one of many things that
could be represented by it).
colorhash_table ppm_alloccolorhash()
This creates a colorhash_table using dynamically allocated storage. There are no colors
in it. If there is not enough storage, throws an error ⟨liberror.html#error⟩ .
void ppm_freecolorhash()
This destroys a ppm_freecolorhash and frees all the storage associated with it.
int ppm_addtocolorhash( colorhash_table cht, const pixel * const colorP, const int value)
This adds the specified color to the specified colorhash_table
and associates the specified value with it.
You must ensure that the color you are adding isn't already present in the
colorhash_table.
There is no way to update an entry or delete an entry from a colorhash_table.
int ppm_lookupcolor( const colorhash_table cht, const pixel * const colorP )
This looks up the specified color in the specified colorhash_table. It returns the
integer value associated with that color.
If the specified color is not in the hash table, the function returns -1. (So if you
assign the value -1 to a color, the return value is ambiguous).
colorhist_vector ppm_colorhashtocolorhist( const colorhash_table cht,
const int ncolors )
This converts a colorhash_table to a colorhist_vector. The return value is a new
colorhist_vector which you must eventually free with ppm_freecolorhist().
ncolors is the number of colors in cht. If it has more colors than that,
ppm_colorhashtocolorhist does not create a colorhist_vector and returns NULL.
colorhash_table ppm_colorhisttocolorhash( const colorhist_vector chv, const int ncolors )
This poorly named function does not convert from a colorhist_vector to a colorhash_table.
It does create a colorhash_table based on a colorhist_vector input, but the integer value
for a given color in the output is not the same as the integer value for that same color
in the input. ppm_colorhisttocolorhash() ignores the integer values in the input. In the
output, the integer value for a color is the index in the input colorhist_vector for that
color.
You can easily create a color map for an image by running ppm_computecolorhist() over the
image, then ppm_colorhisttocolorhash() over the result. Now you can use ppm_lookupcolor()
to find a unique color index for any pixel in the input.
If the same color appears twice in the input, ppm_colorhisttocolorhash() throws an error
⟨liberror.html#error⟩ .
ncolors is the number of colors in chv.
The return value is a new colorhash_table which you must eventually free with
ppm_freecolorhash().
COLOR HISTOGRAMS
The Netpbm libraries give you functions to examine a Netpbm image and determine what
colors are in it and how many pixels of each color are in it. This information is known
as a color histogram. Netpbm uses its colorhash_table data type to represent a color
histogram.
colorhash_table ppm_computecolorhash( pixel ** const pixels, const int cols, const int
rows, const int maxcolors, int* const colorsP )
This poorly but historically named function generates a colorhash_table whose value for
each color is the number of pixels in a specified image that have that color. (I.e. a
color histogram). As a bonus, it returns the number of colors in the image.
(It's poorly named because not all colorhash_tables are color histograms, but that's all
it generates).
pixels, cols, and rows describe the input image.
maxcolors is the maximum number of colors you want processed. If there are more colors
that that in the input image, ppm_computecolorhash() returns NULL as its return value and
stops processing as soon as it discovers this. This makes it run faster and use less
memory. One use for maxcolors is when you just want to find out whether or not the image
has more than N colors and don't want to wait to generate a huge color table if so. If
you don't want any limit on the number of colors, specify maxcolors=0.
ppm_computecolorhash() returns the actual number of colors in the image as *colorsP, but
only if it is less than or equal to maxcolors.
colorhash_table ppm_computecolorhash2( FILE * const ifp, const int cols, const int rows,
const pixval maxval, const int format,
const int maxcolors, int* const colorsP )
This is the same as ppm_computecolorhash() except that instead of feeding it an array of
pixels in storage, you give it an open file stream and it reads the image from the file.
The file must be positioned after the header, at the raster. Upon return, the file is
still open, but its position is undefined.
maxval and format are the values for the image (i.e. information from the file's header).
colorhist_vector ppm_computecolorhist( pixel ** pixels, int cols, int rows, int maxcolors,
int * colorsP )
This is like ppm_computecolorhash() except that it creates a colorhist_vector instead of a
colorhash_table.
If you supply a nonzero maxcolors argument, that is the maximum number of colors you
expect to find in the input image. If there are more colors than you say in the image,
ppm_computecolorhist() returns a null pointer as its return value and nothing meaningful
as *colorsP.
If not, the function returns the new colorhist_vector as its return value and the actual
number of colors in the image as *colorsP. The returned array has space allocated for the
specified number of colors regardless of how many actually exist. The extra space is at
the high end of the array and is available for your use in expanding the colorhist_vector.
If you specify maxcolors=0, there is no limit on the number of colors returned and the
return array has space for 5 extra colors at the high end for your use in expanding the
colorhist_vector.
colorhist_vector ppm_computecolorhist2( FILE * ifp, int cols, int rows, int maxcolors,
pixval maxval, int format, int * colorsP )
This is the same as ppm_computecolorhist() except that instead of feeding it an array of
pixels in storage, you give it an open file stream and it reads the image from the file.
The file must be positioned after the header, at the raster. Upon return, the file is
still open, but its position is undefined.
SEE ALSO
pbm(1), pgm(1), libpbm(1)
AUTHOR
Copyright (C) 1989, 1991 by Tony Hansen and Jef Poskanzer.
DOCUMENT SOURCE
This manual page was generated by the Netpbm tool 'makeman' from HTML source. The master
documentation is at
http://netpbm.sourceforge.net/doc/libppm.html